How do you calculate molar mass?

Add the atomic masses of every atom in the formula, from the periodic table, in g/mol. CO₂: 12.01 + 2 × 16.00 = 44.01 g/mol. C₆H₁₂O₆ (glucose): 6 × 12.01 + 12 × 1.008 + 6 × 16.00 = 180.16 g/mol. If you have measured a mass and know the amount in moles, divide: that is the page's first mode.

How do I convert grams to moles?

Divide the mass by the molar mass. 10 g of water at 18.02 g/mol is 10 ÷ 18.02 = 0.555 mol. Choose 'Moles from mass and molar mass', enter both, and the page shows the division and the number of molecules.

How do I convert moles to grams?

Multiply by the molar mass. 2 mol of CO₂ at 44.01 g/mol is 88.02 g. Choose 'Mass from moles and molar mass'.

What is the difference between molar mass, molecular mass and formula mass?

Molecular or formula mass is the mass of one molecule or formula unit in atomic mass units (amu, u); molar mass is the mass of a mole of them in grams. The numbers are the same — water is 18.02 u and 18.02 g/mol — only the unit changes.

How do I work out a molar mass from a formula?

Multiply each element's atomic mass by how many times it appears and add them. H₂SO₄: 2 × 1.008 + 32.06 + 4 × 15.999 = 98.08 g/mol.

What is Avogadro's number?

6.02214076 × 10²³ — exactly, since the 2019 redefinition of the mole. It is the number of particles in one mole, and the page uses it to turn moles into molecules or atoms.

What is the molar mass of water?

18.015 g/mol: two hydrogens at 1.008 and one oxygen at 15.999. A mole of water is a little over 18 mL.

Molar Mass Calculator (Grams ↔ Moles)

Molar mass from a mass and an amount, or convert grams to moles and moles to grams with a known molar mass, working shown.

Inputs

Find

Mass(g)

0 g1,000,000,000,000 g

Moles(mol)

0 mol1,000,000,000 mol

Molar mass (for the moles and mass modes)(g/mol)

0.001 g/mol1,000,000 g/mol

Add up the atomic masses of the formula: NaCl is 22.99 + 35.45 = 58.44 g/mol.

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Amount of substance

0.0787 mol

Working: 5 g ÷ 63.55 g/mol = 0.0787 mol
Particles: 0.0787 × 6.022 × 10²³ = 4.738e+22
Molar mass used: 63.55 g/mol

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What each Molar Mass input means

Find: Find the molar mass from a mass and an amount, the moles in a mass, or the mass of an amount.
Mass: The mass of the sample in grams.
Moles: The amount in moles.
Molar mass (for the moles and mass modes): The molar mass in g/mol: the sum of the atomic masses in the formula — for water, 2 × 1.008 + 15.999 = 18.015.

Molar Mass formula

molar mass (g/mol) = mass (g) ÷ moles · moles = mass ÷ molar mass · mass = moles × molar mass · particles = moles × 6.022 × 10²³

\mathcal{M} = \frac{m}{n}, \qquad n = \frac{m}{\mathcal{M}}, \qquad N = n \times 6.022 \times 10^{23}

A mole is 6.022 × 10²³ particles, and the molar mass is what one mole weighs in grams — the same number as the formula mass in atomic mass units, which is the point of the definition. For a compound, add up the atomic masses in the formula: water is 2 × 1.008 + 16.00 = 18.02 g/mol, sodium chloride 22.99 + 35.45 = 58.44 g/mol. With the molar mass known, grams and moles convert either way by one division or multiplication, which is the step at the start of nearly every stoichiometry problem. The page does all three: molar mass from a measured mass and amount, moles from grams, and grams from moles, and shows how many particles that is.

Molar Mass worked example

OpenStax's copper example: 5.00 g of copper wire at 63.55 g/mol is 5.00 ÷ 63.55 = 0.0787 mol, which is 0.0787 × 6.022 × 10²³ = 4.74 × 10²² atoms. The other way, 0.25 mol of NaCl (58.44 g/mol) weighs 0.25 × 58.44 = 14.61 g. And if 58.44 g turns out to be exactly one mole, the molar mass is 58.44 ÷ 1 = 58.44 g/mol.

More Molar Mass examples

A quarter of a mole of glucose (C₆H₁₂O₆, 180.16 g/mol): 0.25 × 180.16 = 45.04 g — 1.5 × 10²³ molecules.

An unknown acid: 9.8 g is found to be 0.1 mol, so its molar mass is 9.8 ÷ 0.1 = 98 g/mol — close to sulfuric acid's 98.08 g/mol.

Where the Molar Mass calculator can give the wrong answer

The molar mass must match the formula as written, including water of crystallisation and the state of any ion: CuSO₄·5H₂O is 249.7 g/mol, CuSO₄ is 159.6.
Atomic masses are averages over natural isotopes, so a molar mass to two decimals is as precise as most work needs; isotopically pure samples differ.
Grams to moles assumes a pure sample. Purity below 100% means fewer moles than the arithmetic says.
This page does not parse chemical formulas — you add up the atomic masses yourself, or enter a molar mass from a table. A typo in that number carries straight through.
Molar mass is per formula unit. For ionic compounds 'molecule' is loose language; the count of particles line is formula units.

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Molar Mass reference table

Atomic masses of common elements (g/mol)
Element	Symbol	Atomic mass
Hydrogen	H	1.008
Carbon	C	12.011
Nitrogen	N	14.007
Oxygen	O	15.999
Sodium	Na	22.990
Magnesium	Mg	24.305
Aluminium	Al	26.982
Sulfur	S	32.06
Chlorine	Cl	35.45
Potassium	K	39.098
Calcium	Ca	40.078
Iron	Fe	55.845
Copper	Cu	63.546
Zinc	Zn	65.38

Source: IUPAC standard atomic weights (abridged conventional values)

Molar Mass FAQ

: Add the atomic masses of every atom in the formula, from the periodic table, in g/mol. CO₂: 12.01 + 2 × 16.00 = 44.01 g/mol. C₆H₁₂O₆ (glucose): 6 × 12.01 + 12 × 1.008 + 6 × 16.00 = 180.16 g/mol. If you have measured a mass and know the amount in moles, divide: that is the page's first mode.
: Divide the mass by the molar mass. 10 g of water at 18.02 g/mol is 10 ÷ 18.02 = 0.555 mol. Choose 'Moles from mass and molar mass', enter both, and the page shows the division and the number of molecules.
: Multiply by the molar mass. 2 mol of CO₂ at 44.01 g/mol is 88.02 g. Choose 'Mass from moles and molar mass'.
: Molecular or formula mass is the mass of one molecule or formula unit in atomic mass units (amu, u); molar mass is the mass of a mole of them in grams. The numbers are the same — water is 18.02 u and 18.02 g/mol — only the unit changes.
: Multiply each element's atomic mass by how many times it appears and add them. H₂SO₄: 2 × 1.008 + 32.06 + 4 × 15.999 = 98.08 g/mol.
: 6.02214076 × 10²³ — exactly, since the 2019 redefinition of the mole. It is the number of particles in one mole, and the page uses it to turn moles into molecules or atoms.
: 18.015 g/mol: two hydrogens at 1.008 and one oxygen at 15.999. A mole of water is a little over 18 mL.